Masahiro Nohmi

Attitude control of a tethered space robot by link motion under microgravity

A tethered space robot, which is connected to a mother spacecraft through a peace of tether, is a new space system proposed in the previous work. Expected applications are satellite servicing, inspection of space structure, soft landing, and so on. The tethered subsystem is envisioned to be a multi-body system for a robot, whose attitude can be controlled under tether tension by its own link motion. The tethered subsystem is equilibrium when its mass center is located on the tether extension line. When it deviates from the equilibrium, rotational vibration motion of the subsystem occur due to tether tension. However, the vibration can be suppressed by tether attachment operation of the multi-body subsystem, which can control the tether tension. Characteristics of the proposed attitude control for a tethered space robot has been confirmed by microgravity experiment by using a drop shaft and by parabolic flight of an airplane.

Mission design of a tethered robot satellite “STARS” for orbital experiment

The Space Tethered Autonomous Robotic Satellite (STARS) was developed in Kagawa University and launched by the H-IIA rocket by the Japan Aerospace Exploration Agency (JAXA) on 23 January, 2009. The primary objective of STARS is technical verification of a tethered space robot, which is connected to a mother spacecraft through a tether, proposed in 1995. Main characteristics of STARS are: (i) it is mother-daughter satellite; (ii) it becomes a tethered system on orbit; (iii) the daughter satellite is a tethered space robot. STARS consists of two satellites connected by a tether. One is a mother satellite (a mother spacecraft), which deploys and retrieves a tether connected to the other satellite. The other is a daughter satellite (a tethered space robot). The mother satellite has a tether deployment system. During tether deployment, the attitude of the daughter satellite is controlled by its own arm link motion, and a camera mounted on the daughter satellite takes a photograph of the mother satellite. It is important to design launch lock for STARS, since it has many actuation parts and it is two satellites system.

Microgravity Experiment for Attitude Control of a Tethered body by Arm Link Motion

A tethered space robot, which is connected to a mother spacecraft through a piece of tether, is a new space system proposed in the previous work. The tethered subsystem is envisioned to be a multi-body system for a robot, whose attitude can be controlled under tether tension by its own link motion. This paper discusses about microgravity experiment for attitude control of a tethered space robot. Design and mechanism of the experimental device, required for the proposed attitude control, were explained. Also, link motion control algorithm was designed considering structure of the experimental device. Link motion is controlled for obtaining: (i) torque acting in direction to stable attitude; and (ii) torque damping rotational motion. The proposed control approach was confirmed by two kinds of microgravity experiment. One is by capsule dropping, which can provide high quality microgravity condition during 4.5 seconds. The other is by parabolic flight by an airplane, which can provide 0.01G level condition during 20 seconds. Characteristics of the proposed control approach mounted on the hardware device have been clarified.

Modeling for Lunar Lander by Mechanical Dynamics Software

In the current space development, space explorations are focused on by many space agencies in the world. Next lunar missions will be required to land on steep surface among rocks and craters. For the purpose of lunar soft-landing, dynamics analysis is necessaly especially in contact dynamics with regolith. This paper discusses landing simulation using Mechanical Dynamics Software ADAMS (product by MSC. Software Corp.). Simulation model is based on the lander in the SELENE-B project by Japan Aerospace Exploration Agency. The lander has four landing-gears, and total mass is 400-500kg. Two specific characteristics of simulation model are expressions for honey-comb-core in a landing-gear, and contact dynamics with regolith on the lunar surface. Simulation in this paper especially focuses on influences onsoft-lamding by lander orientation, slope angle, and friction force.

Experimental Analysis for Attitude Control of a Tethered Space Robot under Microgravity

A tethered space robot, which is connected to a mother spacecraft through a peace of tether, is a new space system proposed in the previous work. Expected applications are satellite servicing, inspection of space structure, soft landing, and so on. The tethered subsystem is envisioned to be a multi-body system for a robot, whose attitude can be controlled under tether tension by its own link motion. The tethered subsystem is equilibrium when its mass center is located on the tether extension line. When it deviates from the equilibrium, rotational vibration motion of the subsystem will occur due to tether tension. However, the vibration can be suppressed by tether attachment operation of the multibody subsystem, which can control the tether tension. Characteristics of the proposed attitude control for a tethered space robot has been confirmed by microgravity experiment using a drop shaft, which can provide high quality microgravity condition during 4.5 seconds.

Space teleoperation using force reflection of communication time delay

This paper proposes a new strategy for space teleoperation under communication time delay, which makes it possible for an operator to know conditions of a remote manipulator through force reflection of the time delay. Using the proposed strategy, an operator feels as if the manipulator is operated through a virtual spring. Basic algorithm is that difference of command and telemetry data due to the time delay is displayed to an operator by force reflection of a hand controller. Also, the force reflection includes a contact force applied to the manipulator. In operation without contact, the force reflection becomes to be zero when the manipulator finishes its motion. Under condition of contact, the force reflection continues to be applied even if the manipulator stops its motion. Change of the force reflection suggests: occurrence of contact; force release of the manipulator; and manipulator moving. The effectiveness of the proposed approach was confirmed by teleoperation experiment.

Contact task by space teleoperation using force reflection of communication time delay

This paper proposes a new strategy for space teleoperation under communication time delay, which makes it possible for an operator to know conditions of a remote manipulator through force reflection of the time delay. Using the proposed strategy, an operator feels as if the manipulator is operated through a virtual spring. Basic algorithm is that difference of command and telemetry data due to the time delay is displayed to an operator by force reflection of a hand controller. Also, the force reflection includes a contact force applied to the manipulator. In operation without contact, force reflection becomes to be zero when the manipulator finishes its motion. Under condition of contact, force reflection continues to be applied even if the manipulator stops its motion. Change of force reflection suggests: occurrence of contact; force release of the manipulator; and manipulator moving. The effectiveness of the proposed approach was confirmed by teleoperation experiment, especially focusing on calculation of force reflection and command input.

Solar Paddle Antenna Mounted on Pico-Satellite "KUKAI" for Amateur Radio Communication

This paper describes solar paddle antenna proposed in the development of Kagawa Satellite “KUKAI.” KUKAI is a mother-daughter pico-satellite for technical verification of a tethered space robot. The mother and the daughter satellites communicate respectively with the ground station by amateur radio frequencies. For the purpose of simple deployment system on orbit and antenna directivity suitable for KUKAI, antenna, which communicates with a ground station, mounted at the edge of a solar paddle is employed. After complete antenna adjustment on the ground, KUKAI was launched on 23 January 2009 by the H-IIA rocket from Tanegashima Space Center. The solar paddles were successfully deployed, and communication through the solar paddle antenna was succeeded.

Initial experimental result of pico-satellite KUKAI on orbit

Kagawa Satellite KUKAI has been developed in Kagawa University for technical verification and evaluation of a tethered space robot proposed in 1995. Its technical name before the launch was Space Tethered Autonomous Robotic Satellite (STARS). KUKAI was launched by the H-IIA rocket from Tanegashima, Japan on January 23, 2009. Main characteristics of KUKAI are: (i) it is mother-daughter satellite; (ii) it is a tethered system on orbit; (iii) the daughter satellite is a robot having an arm link. The mother satellite deploys and retrieves a tether connected to the daughter satellite, which is a tethered space robot. During tether deployment, the attitude of the daughter satellite is controlled by its own arm link motion, and a camera mounted on the daughter satellite takes a photograph of the mother satellite. KUKAI was successfully separated from the rocket and transferred into the planned orbit. Normal condition was monitored at the ground station from the housekeeping telemetry, and then the main functions for tether deployment and robotic motion control were verified and evaluated.

Development of Space Tethered Autonomous Robotic Satellite

Space tethered autonomous robotic satellite (STARS) is being developed for technical verification of tethered space robot (TSR), which is a new type of space robot system proposed in the previous work. The STARS consists of mother and daughter satellites connected by tether. The mother satellite deploys tether having the daughter satellite at its end. The daughter satellite is TSR, and has one arm link, whose end is attached to tether. Then, attitude control by arm link motion is possible under condition that tether tension is applied. Main mission of the STARS follows sequence as: the mother satellite release the daughter satellite; attitude of the daughter satellite is controlled by arm link motion; the camera mounted on the daughter satellite takes a picture during deployment; the daughter satellite docks with the mother satellite. The system of the STARS consists of power, data handling, communication, camera, attitude control, structure, deployment, and robotic subsystems. Deployment and robotic subsystems are specific compared to other pico-satellite. Main objective of the deployment subsystem is to deploy and to retrieve tether. On the other hand, main objective of the robotic subsystem is to control attitude of the daughter satellite.